Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Transformer Input/Output PCB design for First Watt PSU - Any good?
Transformer Input/Output PCB design for First Watt PSU - Any good?
Transformer Input/Output PCB design for First Watt PSU - Any good? Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th January 2020, 11:30 PM   #1
Fully Articulated is offline Fully Articulated  New Zealand
diyAudio Member
 
Join Date: Jul 2018
Location: Wellington
Default Transformer Input/Output PCB design for First Watt PSU - Any good?

Hello, I'm here to put my head in the lion's mouth .

I'm configuring a new power supply for an upcoming First Watt clone build, and this time I'd like to experiment a little more with the power section. The plan is to forgo the use of the DIYaudio Universal PSU board and opt for large screw-terminal capacitors in a CLC filter.

While trying to determine a suitable way to mount the rectifers and other components I wondered if I couldn't design a circuit board myself that would sit in-between the transformer and CLC filter. The PCB would mimic the function of the diode boards from the DIYAudio PCB, but instead use monolithic rectifer blocks and include additonal components not specified in the regular First Watt PSU design.

This is what I came up with:

Click the image to open in full size.

The middle section is for 240V AC mains input with provision for one or two thermistors on the live wire for the regular FW-style of inrush current protection, then exits to the primary winding of the transformer. This version also places the 3300pF line filter cap on the board before the thermistors, however I wonder if that be better situated near the main power switch instead.

Flanking the AC input section are the two output sections for the secondary windings. They are designed to incorporate a snubber, plus space for a fuse holder if fusing the secondary is desired. The rectifier blocks are the GPBC-W type with the through-hole leads, hopefully with ample clearance around them for heatsink attachment.

The question: Is this viable, or just rubbish? Opinions or suggestions gratefully received.

Original First Watt PSU, and preliminary new PSU design attached (*asterisks=optional).
Attached Images
File Type: jpg F5PSUschematic.jpg (66.2 KB, 132 views)
File Type: png psu.png (76.2 KB, 136 views)
  Reply With Quote
Old 11th January 2020, 12:47 AM   #2
MorbidFractal is offline MorbidFractal
diyAudio Member
 
Join Date: Nov 2017
Using two thermistors seems to mix the 120/240V versions. You may have a Live to Neutral clearance issue, 3mm. The same might exist Primary Live/Neutral to Secondary, 6mm.

https://www.electricalsafetyfirst.or...1/chargers.pdf

In NZ YMMV
  Reply With Quote
Old 11th January 2020, 01:29 AM   #3
Fully Articulated is offline Fully Articulated  New Zealand
diyAudio Member
 
Join Date: Jul 2018
Location: Wellington
Quote:
Originally Posted by MorbidFractal View Post
Using two thermistors seems to mix the 120/240V versions. You may have a Live to Neutral clearance issue, 3mm. The same might exist Primary Live/Neutral to Secondary, 6mm.

https://www.electricalsafetyfirst.or...1/chargers.pdf

In NZ YMMV

Thanks for your notes. I was particularly concerned about the high voltage primary section. It may be worth dumping that portion altogether.


Although the First Watt PSU specifies one thermistor for 240V operation, some suggest using two in series. The board was designed to give that option.
  Reply With Quote
Old 11th January 2020, 11:53 AM   #4
MorbidFractal is offline MorbidFractal
diyAudio Member
 
Join Date: Nov 2017
It's the two in series that might have been causing clearance issues Live to Neutral. I would expect the component to be sized for the expected inrush versus steady state. I'm not going to guess at the required sums. Presumably two in series gives you a wider range of options and makes the sums harder. I would be inclined to use just one but with a multihole footprint for different sizes.

Having a mains portion on the board is not a bad idea as long as you take care of the clearances. It's nicer for the end user to have the means of mounting the required parts and if you get it right and give the required caveats then they don't have to worry.
  Reply With Quote
Old 11th January 2020, 10:03 PM   #5
Fully Articulated is offline Fully Articulated  New Zealand
diyAudio Member
 
Join Date: Jul 2018
Location: Wellington
You're right I expect. Using one thermistor instead would allow the L to N distance to be increased significantly, although it may be difficult to avoid using two long parallel traces.

I really should have included some measurements in the image. The board is 182x52mm, and the pads & traces are all 3mm. The clearance between the primary and secondaries is 7mm at minimum.

When looking at clearance, do we include the traces below the mask, or is it only the exposed parts to be concerned with? The Live & Neutral traces at the thermistor positions are only 1mm apart, but the exposed pads are much further.

My other concern was whether 3mm traces (at say 2oz) would be enough to handle the current requirements of the amplifier.
  Reply With Quote
Old 12th January 2020, 08:35 AM   #6
Fully Articulated is offline Fully Articulated  New Zealand
diyAudio Member
 
Join Date: Jul 2018
Location: Wellington
Actually I think I can answer that last question with the help of a couple of online calculators.

Taking a worst-case example of an amplifier driving 100W into 2ohm, the required current is 7.07 Amps RMS (provided my maths is correct).

An external 2oz PCB trace of 3mm can do this with a 6.2 deg C rise in temperature above ambient. Sounds good.

Also, traces carrying 240V (340V peak) require 2.31mm clearance, so the input section traces will have to be adjusted.
  Reply With Quote
Old 12th January 2020, 11:01 AM   #7
MorbidFractal is offline MorbidFractal
diyAudio Member
 
Join Date: Nov 2017
Generally a solder mask cannot be used to reduce creepage/clearance distances. It's purpose is just to prevent wetting of otherwise exposed tracks and is subject to damage and poor application. In order to impact creepage/clearance distances you would need to specify a conformal coating which is a different and more expensive beast.
  Reply With Quote
Old 13th January 2020, 03:27 AM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
I wouldn't recommend having components before the fuse.
If they go wrong they can destroy the transformer.
__________________
2020 versions of PCBCAD51, PCBCAD360 and PCBCAD720 out now >>> https://www.murtonpikesystems.co.uk
  Reply With Quote
Old 13th January 2020, 03:43 AM   #9
MorbidFractal is offline MorbidFractal
diyAudio Member
 
Join Date: Nov 2017
Oh. In terms of trace widths knock yourself out and have a go at laying down multiple tracks to build up meaty connections or use your software's fill function to achieve the same. Multiple tracks might be easier and more pleasing to the eye.
  Reply With Quote
Old 13th January 2020, 04:50 AM   #10
Fully Articulated is offline Fully Articulated  New Zealand
diyAudio Member
 
Join Date: Jul 2018
Location: Wellington
Looking further into trace widths led me to this particular page: PCB Trace Width Calculator and Equations which makes a case for the use of the IPC-2152 standard to calculate trace sizes rather than IPC-2221B utilised by the other calculators online.

Taking again the worst-case example of 7Arms current, 6% temp rise with 2oz copper, the width calculates as a whopping 8mm (as opposed to the previous 3mm). Being a bit more sensible by taking the 3.5Arms needed for 50W into 4ohm, the required width then becomes a modest 2.4mm.

Can I assume that duplicating the top layers traces on the bottom layer essentially doubles current carrying capacity?


I think I've jumped in a bit over my head. This appears to be much more difficult than twisting a few wires and connecting them to a terminal block! But more interesting too.
  Reply With Quote

Reply


Transformer Input/Output PCB design for First Watt PSU - Any good?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fs: Plitron, 110 volt input, 750 watt, 80 volt output, toroidal power transformer gaetan8888 Swap Meet 4 17th February 2019 05:40 PM
DAC ouput using Transformer jkeny Digital Line Level 202 13th March 2014 04:19 PM
Removing/Bypassing Headpone ouput a good idea? hearingisbelieving Solid State 8 12th September 2009 09:56 AM
PPI 4100 front input leaking to rear ouput rawadia Car Audio 45 12th February 2009 08:44 AM
balanced ouput to transformer Raj1 Digital Source 4 7th August 2007 10:34 PM


New To Site? Need Help?

All times are GMT. The time now is 02:17 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki